Bumpless semiconductor device

ABSTRACT

When connecting a semiconductor device such as an IC chip with a circuit board by the flip-chip method, a semiconductor device is provided without forming bumps thereon, which enables highly reliable and low cost connection between the IC chip and circuit board while ensuring suppressing short-circuiting, lowering connection costs, suppressing stress concentrations at the joints and reducing damage of the IC chip or circuit board. The bumpless semiconductor device is provided with electrode pads  2  on the surface thereof and with a passivation film  3  at the periphery of the electrode pads  2,  and conductive particles  4  are metallically bonded to the electric pads  2.  Composite particles in which a metallic plating layer is formed at the surface of resin particles are employed as the conductive particles  4.  This bumpless semiconductor device can be manufactured by (a) causing conductive particles to be electrostatically adsorbed onto one face of a flat plate; and (b) overlaying the surface of the plate having the adsorbed conductive particles on the surface of electrode pads of a bumpless semiconductor device which is provided with the electrode pads on the surface thereof and with a passivation film at the periphery of the electrode pads, and ultrasonically welding this assembly, so that the conductive particles are metallically bonded and transferred from the flat plate to the electrode pads.

TECHNICAL FIELD

[0001] The present invention relates to a bumpless semiconductor device.

BACKGROUND ART

[0002] When a bare IC chip is connected to a circuit board by flip-chipmethod, a separation must be provided between the IC chip and thecircuit board in order to prevent occurrence of short-circuiting atscribe lines that are not covered with passivation film. Connectingbumps of height of about 10 μm to 80 μm are therefore commonly formed onthe IC chip (FIG. 3 to FIG. 5).

[0003] In the embodiment shown in FIG. 3, the gold bumps 31 of an ICchip 32 having gold bumps 31 formed by the stud bump method and aconnection terminal 34 of a circuit board 33 are thermo-compressionbonded using an anisotropic conductive adhesive 37 (film or paste)obtained by dispersing conductive particles 35 in a binder 36. Also, inthe embodiment shown in FIG. 4, the gold bumps 41 of an IC chip 42having gold bumps 41 formed by the stud bump method and a connectionterminal 44 of a circuit board 43 are thermo-compression bonded using aninsulating adhesive material 45 (film or paste).

[0004] It should be noted that, in the embodiments of FIG. 3 and FIG. 4,the adhesive force between the IC chip and the circuit board depends onthe coagulative force of the binder (adhesive component) in theanisotropic conductive adhesive (insulating adhesive), since there is nomutual metallic bonding between the bumps 31 (41) and the connectingterminals 34 (44).

[0005] Also, in the case of the embodiment of FIG. 5, connection ofsolder bumps 51 and connecting terminals 54 is achieved by bringing theflux-treated connecting terminals 54 of a circuit board 53 into contactwith the solder bumps 51 of an IC chip 52 formed with solder bumps 51 bya solder paste printing/reflow method or other method, and heating toabove the melting point of the solder, where the gap between the IC chip52 and the circuit board 53 is filled with an underfilling agent 55. Inthis case, usually, a washing operation is performed in order to removethe flux before filling with the underfilling agent 55.

[0006] However, the embodiments of FIG. 3 to FIG. 5 all presuppose theformation of bumps on the IC chip, which are costly to produce, so thereare the problems that the freedom of the IC chip shape is lowered and itis difficult to reduce the cost of effecting connection between the ICchip and the circuit board.

[0007] Since, in the embodiments of FIG. 3 and FIG. 4, no metallicbonding is achieved between the bumps 31 (41) and the connectingterminals 34 (44), the adhesive force between the IC chip and thecircuit board must depend on the coagulative force of the binder(adhesive component) in the anisotropic conductive adhesive (insulatingadhesive). Thus there are the problems that reliability of connection inthe case of the embodiment of FIG. 3 that employs an anisotropicconductive adhesive can be guaranteed, but in the case of the embodimentof FIG. 4, which does not employ an anisotropic conductive adhesive, thereliability of adhesion is lower than in the case of metallic bonding.

[0008] Furthermore, in the case of the embodiment of FIG. 3, withminiaturization of the bump pitch and miniaturization of the bump size,there is the problem that the risk of occurrence of short-circuiting isincreased if the content ratio of conductive particles 35 in theanisotropic conductive adhesive 37 is increased in order to ensure thepresence of such conductive particles 35 between the bumps 31 andconnecting terminal 34. A further problem is that the cost of connectionbetween the IC chip 32 and the circuit board 33 is increased due to thecomparatively high cost of procurement of the conductive particles 35.In the case of the embodiment of FIG. 4, the bumps 41 and connectingterminals 44 are directly press-fixed without interposing conductiveparticles between the bumps 41 and the connecting terminals 44, so thereis a problem of stress concentration at the joints, which further lowersconnection reliability. Also, since the pressure during press-fixingmust be high, there is a possibility of the IC chip or circuit boardsustaining comparatively large-scale damage.

[0009] On the other hand, in the case of the embodiment of FIG. 5,although comparatively satisfactory connection reliability is achieveddue to the metallic bonding between the solder bumps 51 and theconnecting terminals 54, there is the problem that, if the bumps aremade sufficiently large to ensure that metallic bonding is formed, it isdifficult to make finer the pitch of the solder bumps 51. Additionalproblems are that a flux F washing step and underfilling agent 55filling step are added.

[0010] The present invention was made in view of the above problems ofthe prior art. Its object is to make it possible to join an IC chip anda circuit board when connecting a semiconductor device such as a bare ICchip with a circuit board by the flip-chip method, with high reliabilityand low cost without forming bumps on the semiconductor device, whilesuppressing short-circuiting, lowering connection costs, suppressingstress concentrations at the joints and reducing damage of the IC chipor circuit board.

DISCLOSURE OF THE INVENTION

[0011] The present inventors discovered that metallic bonding ofconductive particles exclusively with the electrode pads could beachieved by first electrostatically adsorbing the conductive particleson to a flat plate such as a glass plate, followed by fixing byultrasonic wave pressure in which this surface of the flat plate withconductive particles adsorbed thereon is overlaid with the surface of asemiconductor device on the side of the electrode pads, and therebysucceeded in perfecting the present invention.

[0012] Specifically, according to the present invention, there isprovided a bumpless semiconductor device comprising electrode padsprovided on the surface thereof, and a passivation film formed at theperiphery of the electrode pads, wherein conductive particles aremetallically bonded to the electrode pads.

[0013] Also, according to the present invention, there is provided amethod of manufacturing a bumpless semiconductor device, comprising thefollowing steps (a) and (b):

[0014] (a) a step of causing conductive particles to beelectrostatically adsorbed onto one face of a flat plate; and

[0015] (b) a step of overlaying the surface of the plate having theadsorbed conductive particles on the surface of electrode pads of abumpless semiconductor device which is provided with the electrode padson the surface thereof and with a passivation film at the periphery ofthe electrode pads, and ultrasonically welding this assembly, so thatthe conductive particles are metallically bonded and transferred fromthe flat plate to the electrode pads.

[0016] Furthermore, according to the present invention, there isprovided a connected structure, wherein this bumpless semiconductordevice and a circuit board are joined by an insulating adhesive materialso that conductive particles metallically bonded with the connectingpads of this bumpless semiconductor device may contact the connectionterminals of the circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a diagrammatic cross-sectional view of a bumplesssemiconductor device according to the present invention;

[0018] FIGS. 2(a) to 2(d) are process diagrams for manufacturing abumpless semiconductor device and connected structure according to thepresent invention;

[0019]FIG. 3 is a diagram illustrating a prior art mode of connecting anIC chip and a circuit board;

[0020]FIG. 4 is a diagram illustrating a prior art mode of connecting anIC chip and a circuit board; and

[0021]FIG. 5 is a diagram illustrating a prior art mode of connecting anIC chip and a circuit board.

BEST MODE FOR CARRYING OUT THE INVENTION

[0022] The present invention is further described in detail below withreference to the drawings.

[0023]FIG. 1 is an example in which a bumpless semiconductor deviceaccording to the present invention is applied to an IC chip. This ICchip 1 has a bumpless construction in which electrode pads 2 made of forexample aluminum are provided at the surface thereof and a passivationfilm 3 whose surface position level is higher than the surface positionlevel of the electrode pads 2 is provided at the periphery of theelectrode pads 2. Also, conductive particles 4 are metallically bondedto the electrode pads 2. Consequently, the connection reliabilitybetween the electrode pads 2 and the conductive particles 4 rivals thatof bumps formed on a conventional IC chip as shown in FIG. 3 to FIG. 5.Furthermore, when metallic bonding of the conductive particles 4 to theelectrode pads 2 is effected, metallic bonding can be achieved by acomparatively low-cost technique such as ultrasonic welding, instead ofthe conventional complex and high-cost method of bump forming. Besides,the connection reliability between the conductive particles 4 and theconnection terminals of the circuit board (connected element) iscomparable with the conventional anisotropic conductor connectionmethod, since connection is achieved by the presence of conductiveparticles 4.

[0024] According to the present invention, metallic particles comprisingsolder particles, nickel particles or other particles, or compositeparticles in which a metallic plating layer of, for example, nickel orgold is formed on the surface of a resin particle (core) made of, forexample, benzoguanamine or the like may be employed as the conductiveparticles 4. Of these, use of composite particles with a resin particlecore capable of moderating stress applied to the connected portion ispreferred.

[0025] Regarding the particle diameter of the conductive particles 4,preferably at least some of the conductive particles 4 that aremetallically bonded are of a size such as to project to the outsidebeyond the surface of the passivation film 3. Specifically, preferablythey are larger than the difference of the surface levels of thepassivation film 3 and the electrode pads 2. In this way, occurrence ofshort-circuiting at the scribe lines can be suppressed and theconnection reliability with respect to the element to be connected(circuit board) can be improved. In this case, although the particlediameter of the conductive particles 4 may be made larger than thediameter of the electrode pads 2 in a range such that they are capableof metallic bonding with the electrode pads 2. Preferably, in order tosuppress short-circuiting between the conductive particles 4 in thelateral direction more effectively, the particle diameter of theconductive particles 4 is made smaller than the diameter of theelectrode pads 2. Specifically, the particle diameter of the conductiveparticles 4 is preferably between 1 and 50 μm and even more preferablybetween 3 and 40 μm in the case of metallic particles; in the case of acomposite particles, the diameter of the resin particles is preferably 1to 50 μm and even more preferably between 3 and 40 μm and the thicknessof the metallic plating layer is preferably between 10 nm and 1 μm, oreven more preferably between 15 nm and 1 μm.

[0026] Preferably, in order to reduce contact resistance, a thin goldplating layer of thickness between about 5 nm and 0.5 μm is formed asthe outermost layer of the conductive particles 4.

[0027] As specific constructions of the IC chip 1, electrode pads 2 andpassivation film 3 in the embodiment of FIG. 1, prior art constructionsmay be respectively employed.

[0028] Next, each step of a method of manufacturing a bumplesssemiconductor device (IC chip) according to the present invention willbe described.

[0029] Step (a)

[0030] As shown in FIG. 2(a), first of all, conductive particles 4 asdescribed above are electrostatically adsorbed onto one face of a flatplate 21 such as a flat glass plate. In this case, in order to moreeffectively transfer the conductive particles during ultrasonic weldingin step (b), they are preferably adsorbed as a single layer. As thetechnique for adsorbing the conductive particles 4 electrostaticallyonto the flat plate 21, the surface of the flat plate 21 may beelectrostatically charged by wiping it with a polyester cloth or thelike and the conductive particles 4 then dispersed over the surface.Conductive particles that have not been adsorbed can be removed bytilting or turning over the flat plate 21 or by gently vibrating theflat plate 21.

[0031] Step (b)

[0032] Next, as shown in FIG. 2(b), the surface of the flat plate 21onto which the conductive particles have been adsorbed is overlaid withthe electrode pad surface 2 of an IC chip 1 provided with electrode pads2 on the surface thereof and a passivation film 3 at the periphery ofthe electrode pads 2 and ultrasonic welding is performed preferably fromthe direction of the arrow (FIG. 2(c)). In this way, the conductiveparticles 4 can be transferred from this flat plate 21 to the electrodepads 2 by metallic bonding with the electrode pads 2. It should be notedthat transfer of the conductive particles 4 onto the passivation film 3,which is an insulating film, does not take place, since the conductiveparticles 4 cannot perform metallic bonding therewith.

[0033] As example conditions for welding, there may be mentionedapplication of a frequency between 10 and 100 KHz with a pressurebetween 1 and 100 MPa (per electrode pad) for between 0.1 and 20 sec. Asa specific example of equipment that may be employed, the UltrasonicMicro Welding System (SH40MP, manufactured by ULTAX Inc) can be given.

[0034] Step (c)

[0035] If necessary, any conductive particles 4 that have becomeattached to the passivation film 3 may then be removed by transferringonto commercially available tacky adhesive tape or blowing off byairblow processing, to obtain the bumpless semiconductor device (ICchip) 1 shown in FIG. 2(d).

[0036] With the bumpless semiconductor device (IC chip) 1 shown in FIG.2(d), a connected structure having high connection reliability can beachieved. Specifically, a connected structure (FIG. 2(e)) may bepresented in which a bumpless semiconductor device 1 and a circuit board5 are joined by a known insulating adhesive material 7 in the form of afilm or paste so that conductive particles 4 that are metallicallybonded with the connecting pads 2 may contact the connecting terminals 6of the circuit board 5.

EXAMPLES

[0037] A specific description of the present invention is given belowwith reference to Examples thereof.

Examples 1 to 8 and Comparative Examples 1 to 4

[0038] After wiping one face of a flat glass plate with polyester cloth,the conductive particles of Table 1 were distributed and adsorbed ontothis surface. The excess conductive particles were removed by tiltingthe glass plate and vibrating it gently. In the case of practicalexample 6, metallic particles provided with an Au plated layer on thesurface of an Ni core were employed as the conductive particles but, inthe other practical examples and the comparative examples, compositeparticles in which an Ni plated layer and Au plated layer were formed onthe surface of benzoguanamine (core resin particles) were employed.

[0039] The conductive particles adsorption face of this flat glass platewas overlaid with the electrode pad formation face of a 10 mm square ICchip provided with 500 of aluminum electrode pads on one face thereof ina pitch of 80 μm, and subjected to an ultrasonic welding treatment(frequency 10, 50 or 100 kHz, pressure 49 MPa, treatment time 10 sec),using an ultrasonic welding device (Ultrasonic Micro Welding System(SH40MP, manufactured by ULTAX Inc), from the side of the flat glassplate. The conductive particles were thereby transferred by metallicbonding to the electrode pads of the IC chip. Excess conductiveparticles adhering to the passivation film were blown away by airblowtreatment, to obtain the bumpless semiconductor device (IC chip) shownin FIG. 1. TABLE 1 Conductive particles Ultrasonic Core resin Ni platingAu plating welding particle diameter thickness thickness frequency (μm)(μm) (nm) (kHz) Ex. 1 5 0.15 20 50 Ex. 2 1 0.15 20 50 Ex. 3 50 0.15 2050 Ex. 4 5 0.15 10 50 Ex. 5 5 0.15 1000 50 Ex. 6 10 — 20 50 Ex. 7 5 0.1520 10 Ex. 8 5 0.15 20 100 Comp. EX. 1 0.5 0.15 10 50 Comp. EX. 2 55 0.1520 10 Comp. EX. 3 5 0.15 20 50 Comp. EX. 4 5 0.15 1100 50

[0040] Next, the electrode pads of the bumpless semiconductor deviceobtained were positionally aligned with the connecting terminals(circuit pattern (80 μm pitch) obtained by gold plating onto copper ofheight 8 μm) of a polyimide circuit board of thickness 25 μm, athermo-setting epoxy insulating adhesive film (obtained by removing theconductive particles from anisotropic conductive adhesive film (FP16613,manufactured by Sony Chemicals) was sandwiched therebetween, and theassembly was thermo-compression bonded under the conditions oftemperature 190° C., pressure 1960 kPa, and 10 sec, to obtain aconnected structure.

[0041] When the connected structure obtained was subjected to a thermalshock test (1000 cycles) between −55° C. and 125° C., the connectedstructure using the bumpless semiconductor devices of practical examples1 to 5 and 7 to 8 displayed excellent connection reliability, the risein resistance being in each case no more than 10 mΩ. Also, the rise inresistance of the connected structure employing the bumplesssemiconductor device of Example 6 was about 200 mΩ, which is a levelthat presents no practical problems.

[0042] In contrast, in the case of the connected structure employing thebumpless semiconductor device of comparative example 1, the rise inresistance exceeded 1 Ω, because the core resin particle diameter wastoo small. In the case of the connected structure employing the bumplesssemiconductor device of comparative example 2, the core resin particlediameter was too large, so some of the particles appeared that could notbe carried on the pads, causing the initial resistance value to becomelarge, with the result that this connected structure was unsuitable foruse. In the case of the connected structure using the bumplesssemiconductor device of comparative example 3, the thickness of themetallic plating layer at the surface of the core resin particles wastoo thin, so electrode pads appeared where no conductive particles weretransferred, causing the initial resistance value to become high, withthe result that this connected structure was unsuitable for use. Also,in the case of the connected structure using the bumpless semiconductordevice of comparative example 4, the thickness of the metallic platinglayer at the surface of the core particles was too thick, so theconductive particles coagulated, generating short-circuits.

INDUSTRIAL APPLICABILITY

[0043] According to the present invention, when a semiconductor devicesuch as an IC chip is connected with a circuit board by the flip-chipmethod, the IC chip and the circuit board can be connected with highreliability and low cost while suppressing short-circuits, reducing theconnection cost, suppressing stress concentrations in the joints andreducing damage to the IC chip or circuit board, without forming bumpson the semiconductor device.

1. A bumpless semiconductor device comprising electrode pads provided onthe surface thereof, and a passivation film formed at the periphery ofthe electrode pads, characterized in that conductive particles aremetallically bonded to the electrode pads.
 2. The bumpless semiconductordevice according to claim 1 wherein the conductive particles arecomposite particles in which a metallic plating layer is formed on thesurface of resin particles.
 3. The bumpless semiconductor deviceaccording to claim 2 wherein the diameter of the resin particles isbetween 1 and 50 μm and the thickness of the metallic plating layer isbetween 10 nm and 1 μm.
 4. The bumpless semiconductor device accordingto claim 1 wherein at least some of the conductive particles that aremetallically bonded project to the outside of the surface of thepassivation film.
 5. A method of manufacturing a bumpless semiconductordevice according to claim 1 characterized in comprising the followingsteps (a) and (b): (a) a step of causing conductive particles to beelectrostatically adsorbed onto one face of a flat plate; and (b) a stepof overlaying the surface of the plate having the adsorbed conductiveparticles on the surface of electrode pads of a bumpless semiconductordevice which is provided with the electrode pads on the surface thereofand with a passivation film at the periphery of the electrode pads, andultrasonically welding this assembly, so that the conductive particlesare metallically bonded and transferred from the flat plate to theelectrode pads.
 6. A connected structure comprising a bumplesssemiconductor device according to claim 1 and a circuit board, whereinthe bumpless semiconductor device and the circuit board are joined by aninsulating adhesive material so that conductive particles metallicallybonded with the connecting pads of this bumpless semiconductor devicecan contact the connection terminals of the circuit board.
 7. Thebumpless semiconductor device according to claim 2 wherein at least someof the conductive particles that are metallically bonded project to theoutside of the surface of the passivation film.
 8. The bumplesssemiconductor device according to claim 3 wherein at least some of theconductive particles that are metallically bonded project to the outsideof the surface of the passivation film.
 9. A method of manufacturing abumpless semiconductor device according to claim 2 characterized incomprising the following steps (a) and (b): (a) a step of causingconductive particles to be electrostatically adsorbed onto one face of aflat plate; and (b) a step of overlaying the surface of the plate havingthe adsorbed conductive particles on the surface of electrode pads of abumpless semiconductor device which is provided with the electrode padson the surface thereof and with a passivation film at the periphery ofthe electrode pads, and ultrasonically welding this assembly, so thatthe conductive particles are metallically bonded and transferred fromthe flat plate to the electrode pads.
 10. A method of manufacturing abumpless semiconductor device according to claim 3 characterized incomprising the following steps (a) and (b): (a) a step of causingconductive particles to be electrostatically adsorbed onto one face of aflat plate; and (b) a step of overlaying the surface of the plate havingthe adsorbed conductive particles on the surface of electrode pads of abumpless semiconductor device which is provided with the electrode padson the surface thereof and with a passivation film at the periphery ofthe electrode pads, and ultrasonically welding this assembly, so thatthe conductive particles are metallically bonded and transferred fromthe flat plate to the electrode pads.
 11. A method of manufacturing abumpless semiconductor device according to claim 4 characterized incomprising the following steps (a) and (b): (a) a step of causingconductive particles to be electrostatically adsorbed onto one face of aflat plate; and (b) a step of overlaying the surface of the plate havingthe adsorbed conductive particles on the surface of electrode pads of abumpless semiconductor device which is provided with the electrode padson the surface thereof and with a passivation film at the periphery ofthe electrode pads, and ultrasonically welding this assembly, so thatthe conductive particles are metallically bonded and transferred fromthe flat plate to the electrode pads.
 12. A connected structurecomprising a bumpless semiconductor device according to claim 2 and acircuit board, wherein the bumpless semiconductor device and the circuitboard are joined by an insulating adhesive material so that conductiveparticles metallically bonded with the connecting pads of this bumplesssemiconductor device can contact the connection terminals of the circuitboard.
 13. A connected structure comprising a bumpless semiconductordevice according to claim 3 and a circuit board, wherein the bumplesssemiconductor device and the circuit board are joined by an insulatingadhesive material so that conductive particles metallically bonded withthe connecting pads of this bumpless semiconductor device can contactthe connection terminals of the circuit board.
 14. A connected structurecomprising a bumpless semiconductor device according to claim 4 and acircuit board, wherein the bumpless semiconductor device and the circuitboard are joined by an insulating adhesive material so that conductiveparticles metallically bonded with the connecting pads of this bumplesssemiconductor device can contact the connection terminals of the circuitboard.